Method for production of malleable and annealable nickel direct by electrolysis



Patented Apr. 26, 1938 UNITED STATES PATENT OFFICE ELECTROLYSIS AntonMartin Gronningsaeter, Crestwood, N. Y., assignor to Falconbridge NickelMines Limited, Toronto, Ontario, Canada No Drawing. Application January7, 1935, Se-

rial No. 591. In Norway January 15, 1934 1 Claim.

In electrolytic metal refining the metal obtained is usually resmeltedbefore passing through the further operations necessary to turn out afinished product. It is evident that it is desir- 5 able to produce themetal in such form and with such properties that this resmelting andpart of the further fabricating work on the smelted material can beomitted. It is a generation since experiments were started with directproduction of copper pipes and copper sheets by electrolysis, but onlyvery recently has such manufacture of copper sheets reached anyimportance. Experiments which have been made with production of ironpipes by electrolysis have so far not reached commercial importance.

Nickel sheets (and pipes) are now made by smelting nickel to ingotswhich are mechanically worked, in a way similar to that for iron, intosheets, pipes, wire, etc., a prpcedure involving quite considerableexpense, because nickel is not easy to work. It has also been proposedto produce nickel direct by electrolysis, which, without resmelting andeasier than with ingots produced by smelting, can be worked into sheets,etc. Particularly in late years, when the. nickel electrolysis has comeunder much closer control than before, considerable experimenting hastaken place in this field, but the results obtained have not gained anyconsiderable practical importance. 1

m The reason for this is partly the high extra costs for production, andpartly the uncertain and less satisfactory technical results. For theexperiments made, nickel as a rule has been resmelted and used as anodesin a bath, where under special 35 conditions a malleable nickel has beendeposited;

v this, as will be seen, is no attempt to get a satisfactory productfrom nickel produced direct as a step in the refining process proper.Partly, it

has also been assumed that the use of rotating cathodes would benecessary; under such conditions the extra costs would of course becomparatively high. v

The aim of the present invention has been to find a method by which itis possible in connection with the refining process to obtain a productwhich is suitable for further mechanical working. The method permitsproduction. of nickel sheets of approximately the dimensions desired. Itis therefore only necessary to give these a quite simple rollingtreatment in order to get the desired exact dimensions, and in order toget a satisfactory surface. The sheets obtained are, after annealing, ifdesired, ready for the trade. A product for the trade is thereforeobtained by a very simple rolling operation, followed if desired byannealing.

The requirements for a are the following:

The material for the trade must not only be malleable, but must alsoafter possible annealing have the mechanical properties that arenecessary for further fabricating operations. Further, the surface ofthe finished product must satisfy the demands of the trade. Hitherto, ithas been diflicult with certainty to make a material which afterannealing satisfies the demands of the users as to strength andabilityto stand mechanical working. Furthermore, the nickel produced hashad a tendency during the electrolytic deposition to form growths on thesurface thus spoiling the same. The difficulties have been overcome byproper attention during the production of the nickel to the factorsdescribed in the following:

Of decided importance for obtaining the results desired is that thedeposition of nickel takes place under such conditions that a nickel ofextraordinary purity is deposited. Harmful impurities are metals, as forinstance, arsenic and lead. Other impurities possibly even worse aresatisfactory product organic matter, hydrogen and mechanically oceludedhydroxides,.basic salts, and electrolyte; in short all substances whichby annealing destroy the structure ofthe metal. The special purity ofthe nickel may conveniently be obtained by using a process as describedin my copending applications Serial Nos. 487,369, filed October 8, 1930and 685,226, filed August 15, 1933 by which process the electrolyte isfirst treated with gas re-- duced nickel to precipitate copper, and toneutralize free acid, thereafter blown with air to precipitate iron byoxidation and hydrolysis, and then passed through an electrolyticpurification process whereby the largest part of the remaining metallicimpurities are deposited with, and concentrated in a small amount of thenickel, and perhaps finally blown further with air for completeprecipitation of iron. After this treatment, the electrolyte may be usedfor the deposition of a larger amount of nickel, which according to thismethod may have a very high purity so far as the metallic impurities areconcerned.

This purification operation also tends to remove organic matter. As tohydroxides, basic salts and hydrogen, the content in the nickel of thesemay be controlled by usinga pH for the electrolyte suitable for thetemperature and current density used. Sinceizhe hydrogen contentinihe,

' other oxidizing-agents that. are not harmful forsible; but it must onthe other hand not be so high that there is a risk of precipitating outhydrox'ides and basic salts by hydrolysis. Since iron hydrolizes easily,it is of special importance that the electrolyte used have the lowestpossible iron content. It has been found that better results areobtained by using a lower temperature than has heretofore been used fornickel electrolysis. It has for instance been proved that underotherwise identical conditions, the nickel obtained is considerablysofter at 40 C. than at 55 C. The reason for this-is believed to be thatthe nickel deposited at lower temperatures contains less hydrogen. Bythe above mentioned purification process, organic matter is removed bothby the electrolytic purification and by the blowing with air to removeiron. In many cases it is favorable'to remove organic matter morecompletely, and this can be done by finally giving a further oxidizingtreatment with air, hydrogen peroxide, potassium permanganate, or

the later. electrolytic deposition of nickel. Without daring to say thata complete explanation of the phenomena has been given, it can be statedthat by a method as described a malleable metal may be obtained whichcan stand annealing and still retain satisfactory mechanical properties.

Another main difliculty to overcome in the manufacture is growths on theelectrolytically deposited nickel. While uneveness on the surface of themetal, on which deposition has taken place, will show, this is not animportant difllculty. The dimculty is in growths on the-surclearelectrolyte with especially low iron content and using a suitable pH,temperature and current density to produce nickel on stationary cathodeswith a sufliciently smooth surface, something of the greatest importancefor the economyof the process. I

' A highly purifiednickel electrolyte, containing at best only traces ofimpurities that work against a malleable and annealable product and asmooth surface, mustbe'employed in the making of the cathodes. pointedout insai'd copending applications, an acidic nickel-copper electrolyte,containing an objectionableamount of iron in solution, is subjected tothe neutralizing and copper-cementingacti'on of finely-divided,highly-reactive, metallic nickel powder obtained bygas" reduction at atemperature only slightly the electrolyte without the introduction ofany other neutralizing agent. The electrolyte is above that "required toefiect reduction. The

highly reactive nickel is sufiicient in amount and reactivity to effectsubstantial neutralization of filtered to remove copper, arsenic, andaccompanying solids. The electrolyte thus neutralized is advantageouslysubjected to aeration to effect precipitation by oxidation andhydrolysis of substantially all of the objectionable iron present.

relative movement is advantageously effected between the electrolyteandthe cathode during the the nickel and a relatively large amount of theThe current density impurities on the cathode. and the amount of currentemployed are regulated to effect neutralization of the electrolyte tosuch a degree that a small amount of iron still present may be morereadily precipitated by oxidation and hydrolysis. The neutralizedelectrolyte may then be subjected to aeration to effect precipitation ofsubstantially all of the remaining objectionable iron, and filtered toremove the pre cipitated iron.

i It will, of course, be clear to those'skill'ed in this art that anyother effective procedure may be employed to'remove harmful impuritiesin order to obtain a highly purified electrolyte, which is required inthe practice of the present'invention.

The highly purified electrolyte is then subjected to the mainelectrolysis step in'the nickelrefining operation. The. temperature andpH- value of the electrolyte and the current density are so correlatedin relation one to' the other as to inhibit the formation of hydroxidesand hydrogen. The pH of the electrolyte is maintained substantially ashigh as possible without precipitation of hydroxides and'basic salts ofthe impurities, including hydroxides and basic salts of nickel, areprecipitated by hydrolysis to inhibit the occlusion of hydroxides in thecathodes and to inhibit 'th'e formation of berries. The

temperature of the electrolyte is preferably maintained within a rangeof about 2545 C. A current density is employed that is sufliciently lowto inhibit the growth of berries on the cathodes.

A few examples of specific applications of the invention are herewithpresented. It will, of course, be understood that they are merelyillustrative and that the invention-is not to be thereby restricted.

' Example 1 v The process is carried out in connection with the nickelrefining process as described in'my above mentioned. applications.Thereby is obtained a nickel with 99.98+Ni(+Co.). A purification carriedto the extreme is not always neces sary, but improves the obtainedmetals quality. To the electrolyte purified in this way, .and filtered,is added a little hydrogen peroxide.

Electrolytic deposition takes place on aluminum favorable.

Example 2 A nickel electrolyte is given such ascomplete purificationtreatment by known ,methods that nickel deposited therefrom containsless than 0.01% of arsenic, antimony, tin, bismuth, lead,

hydrogen, sulphur; selenium and tellurium com.- bined. Then theelectrolyte at C. is given a treatment with potassium permanganatewhereby most of its content of organic matter is oxidized away; afterfiltering and cooling to 25 C., sulphuric acid is added to bring the pH.to 5.7. From this electrolyte nickel is deposited at a current densityof 0.6 ampere per dm.

. Example 3 An electrolyte for use for electrodeposition of ordinarynickel is purified by methods described 75 in the above mentionedapplications. A part of this electrolyte, to be used for production ofmalleable annealable nickel, is given a renewed electrolytic treatmentfor further removal of copper, arsenic, lead and other metal impuritiesfollowed by another oxidation by blowing with air in order to lowerfurther its content of organic matter and iron. The electrolyte is thenfiltered and sulphuric acid added to regulate the pH to 5.6 and thetemperature lowered to 45 C. The iron content of the electrolyte isafter this treatment so low that the nickel obtained by the followingelectrolysis contains less than 0.002% iron.

I claim:

In the method of producing malleable and annealable nickel cathodes byelectrolytic deposition directly from nickel sulfate electrolytesemployed in nickel refining operations, the steps which comprisesubjecting a highly purified nickel electrolyte, containing traces onlyof impurities which conventionally are removed, to electrolyticdeposition at a temperature of from about 25 C. to 45 C. at a currentdensity not substantially exceeding one ampere per square decimeter, andmaintaining the pH of the electrolyte as high as possible withoutprecipitation of hydroxides and basic salts by hydrolysis.

